Dean Jackson made this change downstream in WebKit:
https://bugs.webkit.org/show_bug.cgi?id=216722

Change ANGLE to dynamically load either EAGL (OpenGLES) or CGL (OpenGL)
depending on both compile and runtime configurations.
    Intel Mac -> CGL
    Intel Mac Catalyst -> CGL
    Intel iOS Simulator -> EAGL
    iOS Device -> EAGL
    Apple Silicon Mac -> CGL
    Apple Silicon Mac Catalyst (with Mac app) -> CGL
    Apple Silicon Mac Catalyst (with iOS app) -> EAGL

The trickiest bit is Apple Silicon Mac Catalyst, which depends on the
type of the application it is attempting to run. In that case ANGLE must
compile both the CGL and EAGL interfaces and then pick one to use after
launch.

Bug: angleproject:5253
Change-Id: Iba167b3cc3105e457dcfc9bc14147d0fc3e70bac
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2500185
Commit-Queue: James Darpinian <jdarpinian@chromium.org>
Reviewed-by: Geoff Lang <geofflang@chromium.org>
Reviewed-by: Kenneth Russell <kbr@chromium.org>